A first isochronous coder-decoder (“codec”) generates a stream of frames in a periodic sequence. The first isochronous coder-decoder in one example sends the stream to a second isochronous coder-decoder. The second isochronous coder-decoder expects the stream of frames to be in the periodic sequence. For example, isochronous code division multiple access (“CDMA”) codecs produce a stream that comprises a voice frame every 20 milliseconds. Isochronous code division multiple access codecs produce frames of various sizes/rates for transmission on the code division multiple access air interface. The sizes/rates of the frames in one example comprise full rate, half rate, quarter rate, and eighth rate. For example, the eighth rate frames are the smallest frames produced by the isochronous code division multiple access codec. The isochronous code division multiple access codecs use the eighth rate frames to transmit low volume audio signals, for example background noise in a voice conversation. Exemplary isochronous code division multiple access codecs comprise enhanced variable rate codec (“EVRC”), 13-kilobit version (“13 k”), and selectable mode vocoder (“SMV”).
A real time protocol, user datagram protocol, and internet protocol stack (“RTP/UDP/IP”) is a transport protocol stack for packet media. Each frame transported via RTP/UDP/IP comprises a data portion and a header portion. The RTP/UDP/IP header portion is a substantial amount of information. Therefore, even a frame with a very small data portion has a substantial amount of information to transmit. For example, an eighth rate frame transmitting only background noise over RTP/UDP/IP requires a header portion of the frame with a substantial amount of information.
As one shortcoming, the near constant transmission of frames with a substantial amount of information between isochronous codecs diminishes the transport efficiency of the air interface and backbone network. During a voice call there will be times when at least one of the isochronous codecs involved in the voice call will generate a frame corresponding to silence. The silence can be represented with a relatively small amount of information in the data portion. However, the RTP/UDP/IP header portion added to the data portion makes the total size of the frame large and thus, taxing to the resources of the air interface and backbone network.
Thus, a need exists to increase a transport efficiency of isochronous codec data transmissions.